In this article, we share our experience as we tried to fix a blown head gasket by using a sealer instead of replacing it. In our case, we have a Mazda 5 with a blown head gasket. Here you will learn how we confirmed that we had a blown head gasket and typical symptoms of a bad head gasket. 

Since it doesn't make sense to spend thousands of dollars on replacing the head gasket, a labor-intensive job, we went the route of trying to fix it by using a head gasket sealer. 

We were determined to find out the best head gasket sealer on the market. Price wasn't an issue since the alternative solution would be to replace the head gasket which can cost from $1500 up to $3500 in some cases which doesn't make sense in an old car. 


In our case, we had a car with several symptoms you would expect from a blown head gasket. When you have a blown head gasket coolant leak and get into the oil galleries, leak out of the engine or leak into the cylinders. 

Coolant was getting into the cylinders. In our case, we didn't notice oil mixing with coolant but it was probably still happening in small amounts, and an oil test could confirm this.  

Low Compression

blown head gasket

One of the methods used to confirm a blown head gasket is checking engine compression. In this case, we got 90 psi in several cylinders. That's very low. In a healthy engine, you need to get around 150 psi per cylinder.

Bubbles in the radiator

symptoms of blown head gasket bubbles

A common symptom of a blown head gasket is bubbles in the radiator overflow tank or radiator. This is something you can check yourself and doesn't require any tools. Don't open the radiator cap if the engine is hot. 

White smoke

blown head gasket seaer symptoms

A blown head gasket engine can cause coolant to get into the cylinders. It will foul the spark plugs and your car will crank but not start. If you can get the car to start by cranking it for a long time (not recommended), the coolant may enter the cylinder ending up coming out of the exhaust as white smoke/steam and in extreme cases even liquid. 

Fouled Spark Plugs

blown head gasket repair fix sealant instructions seal

Coolant can get into the cylinders. When we removed the spark plugs we noticed the spark plugs were fouled. We dried them and reinstalled the spark plugs back into the engine. This was the only way we could get the car to run again. If the car was turned off after a while coolant would reenter the cylinders, and we couldn't start the engine again.

Choosing a good head sealer

Choosing a head gasket sealer that works isn't easy when there are too many head gasket sealants on the market.

  1. Steal Seal head gasket repair
  2. Blue Devil head gasket sealer
  3. Bar's Leak head gasket sealant
  4. K-Seal Coolant Leak Repair
  5. CRC Head Gasket & Block Repair

This is only a few of the most popular head gasket sealers and there are many more sealers not listed here. No wonder that trying to choose a head gasket sealant can get confusing.  

BlueDevil Head Gasket Sealer

BlueDevil is one of the best-rated head gasket sealers on sites like Amazon. This is how it works. It requires that you partially drain the coolant. Remove the thermostat. The thermostat needs to be removed to allow the sealer to flow through the engine block. Next, you need to reinstall everything, and add the head gasket sealer and let it do its work. Finally drain the coolant again, reinstall the thermostat, flush and refill with 50/50 antifreeze. 

Bar's Leak Head Gasket Sealer 

We also considered the Bars Leak head gasket sealer which doesn't require the removal of the thermostat or the coolant to be flushed. Add it directly to your radiator, no extra steps. Not only that but it has additives that create an artificial carbon fiber gasket according to the manufacturer. The manufacturer claims it should work with wrapped heads, blown head gaskets and fix head gasket leak.

Which head gasket sealer did we pick?

After several hours reviewing different gasket sealers, specifications, application methods and user reviews we narrowed our search to two gasket sealants. 

do blown head gasket sealer repair work

Out of all the head gasket sealers we reviewed, we picked Bar's Leak HG-1 head gasket sealer. One of the main advantages of this gasket sealer is that it is simple to use. It can be applied without having to remove the thermostat. 

Why we choose Bar's Leak? 

  • Designed to fix head gaskets 
    • also for intake gaskets
  • Meant to work on warped head or block
    • We suspect our Mazda5 has a warped head because we are getting low compression on more than one cylinder. It is impossible to test for a warped head without removing it.
  • Stop overheating and coolant loss
    • Our car was leaking coolant into two cylinders. 
    • Our Mazda5 would overheat after 15 minutes.
  • Fix bubbles entering the cooling system
    • Our test car had bubbles entering the cooling system, see video below. 

Bar's Leak makes several head gasket sealers with varying degrees of strength. Their strongest and best product is Bar's Leak HG-1 Head Seal.

Bar's Leak also makes other gasket sealers such as Block Seal and Head Gasket Fix sealant. One of the main advantages of HG-1 is that it creates a carbon fiber layer when it sets. It also can be left in the cooling system which allows it to stop small head gasket leaks over time. 


Adding the head gasket sealer is easy. Make sure to follow the instructions that come with your particular head gasket sealer. Below are the steps we followed to install Bar's Leak Head Gasket Sealer. 

  1. Allow the engine to cool down.head gasket sealer instructions


  2. Removed the radiator cap.head gasket sealer for boats cars motorcycle
    Shake the bottle. Add it based on the dosage chart found on the box. head gasket sealer dosage bars leak head seal aluminum


  3. Add head gasket sealer to the radiator.head gasket fixFilled reservoir with coolant. Fill overflow tank to reach a level between the Min and Max mark. 
  4. Reinstall the radiator cap.blown cylinder head gasket


  5. Start the engine. If the engine doesn't start at first try, wait 15 seconds and try again. start car using head gasket stop leak


  6. Turned the heat on. Make sure it is set to HOT setting even if it is summer. 
  7. Let the engine idle until the temperature reaches normal operation. In most cases, this takes about 15 to 20 min in idle. Let the engine run for another 10 min. Total run time of 30 min. 
  8. We allowed the engine cool down overnight. 


  • Make sure to add coolant if the level is low.
  • Do not allow the engine to overheat.
  • If your temperature gauge goes to red, turn off the engine and let it cool down. 

Updates 1

Ok, so you want to know the results. Did the head gasket sealer work? 

At the start of this test, we had 32080 miles on the car.

Check out how the coolant overflow reservoir looked before applying the head gasket sealer. 


The next morning, as we tried to start the car, it would turn over but not start. Not good. 

We removed the spark plugs. A couple of them have fouled again. Dried the spark plugs and reinstalled. 

This time the engine started. 

Next, we checked for bubbles in the coolant overflow reservoir.

While the head gasket wasn't completely fixed you can see that the air bubbles had reduced and required a flashlight to be noticed.

Since the head gasket sealer was starting to have an effect we decided to repeat the procedure a couple more times but without having to add any more additive. We would start up the car, run it for thirty minutes and then let it cool down. We would let the engine warm-up, turn it off, let it cool down and repeat a few times. What this does, it allows the sealer to get in places where it didn't get before. We are slowly building up a new "head gasket". At first, we had to remove the spark plugs and dry them because the coolant was still getting into the cylinders. Eventually, the car would start right up without needing to remove the spark plugs. 

Update 2

The head gasket sealer is still working. Mileage as of October 2017, 32252 miles.

do head gasket sealers work

Update 3

It is now November and the car has nearly 32450. Unfortunately, it has started to foul the spark plugs again and the engine struggles to start. This is an indication that the head gasket sealer has started to fail. 

So, do head gasket sealers really work? 

It really depends on how and where your head gasket has failed. This test is one particular case and doesn't guarantee that you will get the same results. It may not work at all or the sealer may stop the head gasket leak on the first try.

In our case, the head gasket did slow down the coolant leak. Eventually, the head gasket leak returned.

We believe that even if the sealer works, using a head gasket sealer is only a temporary fix. Your head gasket problems may return sooner or later. It may last three weeks or three years. There is no way guarantee.

There may be other head gasket sealants that work just as well as Bar's Leak. It's up to you to decide which is the best head gasket sealer. This tutorial was not written to promote one product over another. 

Tested product was purchased and not sponsored by the manufacturer.